Ionic compounds are compounds that are composed of ions i.e., cations and anions. Ionic compounds are suitable for use as a catalyst and as a solvent in alkylation reactions, polymerization, dimerization, oligomerization, acetylation, metatheses and copolymerization reactions.
The most common ionic compounds are those prepared from organic based cations and inorganic or organic anions. Pyridinium and imidazolium are frequently used cations whereas anions such as BF4−, PF6−, haloaluminates such as Al2Cl7− and Al2Br7−, [(CF3SO2)2N)]−, alkyl sulphates (RSO3−), and carboxylates (RCO2−) are commonly employed. The catalytically interesting ionic compounds are those derived from ammonium halides and Lewis acids such as AlCl3, TiCl4, SnCl4, FeCl3.
Haloaluminate ionic compounds are ionic compounds derived from ammonium halides and AlCl3 which are used for alkylation reactions. For instance, 1-butyl-3-methyl imidazolium bromide can be reacted with AlCl3 to form fused [BMIM]Al2Cl6Br ionic compound which is used as a catalyst for alkylation reactions. Conjunct polymers are formed as by-products during the alkylation reactions employing ionic compound catalysts. These by-products deactivate the ionic compound catalyst by forming complexes with the ionic compound catalyst. The activity of the ionic compound catalyst decreases with repeated use of ionic compound catalyst which after a certain number of recycles needs to be replaced. Deactivation of ionic compound catalyst by by-products is problematic and adversely affects the economics of alkylation reactions. Therefore, commercial exploitation of ionic compound catalysts for alkylation reaction would be economical only if they can be efficiently regenerated and recycled.
Few methods were reported for removing the conjunct polymers and regenerating the ionic compound catalysts.
U.S. Pat. Nos. 7,651,970, 7,678,727, 7,691,771 and 7,884,045 disclose a process for regenerating a used chloroaluminate ionic liquid catalyst. The process consists of contacting the used chloroaluminate ionic liquid catalyst and hydrogen with a metal or homogeneous or supported hydrogenation catalyst in a reaction zone under hydrogenation conditions for a time sufficient to reactivate the ionic liquid catalyst.
U.S. Pat. No. 7,674,740 discloses the regeneration of used ionic liquid by contacting it with an iso-paraffin containing stream and Bronsted acid in a reaction zone.
U.S. Pat. No. 7,732,364 and WO 2009/085450 disclose the regeneration of used ionic liquid by contacting it with Aluminium metal in the presence of hydrogen to liberate conjunct polymers. United States Patent No. 20100278699 discloses the above method in a reactive extraction column.
WO 2001/15175 discloses the regeneration of imidazolium based ionic liquid such as 1-methyl-3-ethylimidazolim by subjecting it to thermolysis at 250° C. for 3 hrs at 2 mm Hg.
U.S. Pat. No. 7,737,067 discloses regeneration of deactivated 1-Butyl-pyridinium heptachloroaluminate by adding 1-Butyl-pyridinium chloride along with inert hydrocarbon ranging from C5 to C8. 1-Butyl-pyridinium chloride interacts with AlCl3 species thereby liberating the conjunct polymer. The conjunct polymer thus released simultaneously gets solubilized in inert hydrocarbon layer. The 1-Butyl-pyridinium heptachloroaluminate obtained is further treated with AlCl3 to fully restore the activity of the catalyst.
U.S. Pat. No. 7,956,002 discloses the method for regenerating an used acidic ionic liquid catalyst. The method consists of contacting the used ionic liquid catalyst with at least one metal in a regeneration zone in the presence of hydrogen under regeneration conditions for a time sufficient to activate the ionic liquid. The regeneration of the used ionic liquid can also be conducted in the presence of a hydrocarbon solvent.
U.S. Pat. No. 8,088,338 discloses an apparatus for regenerating an ionic liquid catalyst which has been deactivated by conjunct polymers. The apparatus consists of moving bed wherein slurry of ionic liquid and aluminium metal can be feed. Solvent and hydrogen gas (optional) are feed through the bottom of the reactor which remove conjunct polymer and regenerates the ionic liquid.
U.S. Pat. No. 8,597,517 discloses a process for regeneration of ionic liquids after being used as an extracting agent for sulfur compounds. The process involves dissolving the ionic liquid in acetone, adjusting the pH with sodium hydroxide to form a precipitate, filtering the solution to remove the precipitate from the solution, removing the solvent from the filtrate by evaporation under reduced pressure, dissolving the residue obtained in acetone, filtering the solution to remove the precipitate, adjusting the pH of the solution by adding hydrochloric acid to a pH range of 2-7 and heating the regenerated ionic liquid to 70-80° C., under reduced pressure until dry. The process disclosed in U.S. Pat. No. 8,597,517 employes strong base such as sodium hydroxide which precipitates aluminium as Al(OH)3 and generates HCl. Thus, recovering and recycling of aluminium trichloride is difficult.
The drawbacks associated with the processes of the prior art are that the purity of the catalyst recovered/regenerated is poor and cannot be reused/recycled beyond certain limit. Further, some of the processes require specialized apparatus leading to heavy investments in equipment. Still further, in some of the prior art processes, the conditions employed are severe and therefore, energy inefficient.
Therefore, there is felt a need for a simple and economic process for regenerating ionic compound having high purity and recycleability and which utilizes alternative solvents and bases which can be employed to effectively regenerate the ionic compound.
Objects:
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
It is an object of the present disclosure to provide a process for regenerating ionic compound.
It is another object of the present disclosure to provide a process for regenerating ionic compound which is efficient, simple and economic.
It is still another object of the present disclosure to provide a high yielding process for regenerating ionic compound.
It is still another object of the present disclosure to provide a process for regenerating ionic compound having high purity.
Other objects and advantages of the present disclosure will be more apparent from the following description, which are not intended to limit the scope of the present disclosure.